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            <li>
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                <span>产品技术部</span>
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                    <li><span>产品小组</span></li>

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                        <span>UI小组</span>
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                                <span>UI设计师</span>
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                        <span>开发小组</span>
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                                <span>前端开发</span>
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                                    <li><span>pc设备开发</span></li>
                                    <li><span>移动设备开发</span></li>
                                    <li><span>VR开发</span></li>
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                                        <span>NODE开发</span>

                                    </li>
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                            <li><span>后台开发</span></li>
                            <li><span>服务器开发</span></li>
                            <li><span>公共技术研发团队</span></li>
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                    <li><span>测试小组</span> </li>
                    <li><span>运维小组</span></li>
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            <li>
                <!-- 每个li有且只有一个span,如果有下一级才有em ul -->
                <!-- plus + minus - -->
                <em class="plus"></em>
                <span>产品技术部</span>
                <ul class="level2">
                    <li><span>产品小组</span></li>

                    <li>
                        <em class="plus"></em>
                        <span>UI小组</span>
                        <ul class="level3">
                            <li>
                                <span>UI设计师</span>
                            </li>
                            <li>
                                <span>UE体验师</span>
                            </li>
                        </ul>
                    </li>

                    <li>
                        <em class="plus"></em>
                        <span>开发小组</span>
                        <ul class="level3">
                            <li>
                                <em class="plus"></em>
                                <span>前端开发</span>
                                <ul class="level4">
                                    <li><span>pc设备开发</span></li>
                                    <li><span>移动设备开发</span></li>
                                    <li><span>VR开发</span></li>
                                    <li>
                                        <span>NODE开发</span>

                                    </li>
                                </ul>
                            </li>
                            <li><span>后台开发</span></li>
                            <li><span>服务器开发</span></li>
                            <li><span>公共技术研发团队</span></li>
                        </ul>

                    </li>

                    <li><span>测试小组</span> </li>
                    <li><span>运维小组</span></li>
                </ul>
            </li>

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